DESCRIPTION: (Scanned from the applicant's abstract) The proposed experiments will test the hypothesis that alterations in the cell cycle during ovarian follicle development modulate the susceptibility of follicle cells to undergo apoptosis. These changes affect critical stages of follicle development including (1) selection of the dominant follicle for development to the ovulatory stage and (2) terminal differentiation of granulosa cells after the preovulatory luteinizing hormone (LH) surge. Our previous work demonstrated the presence of a functional Fas antigen (Fas) pathway in the ovarian follicle. Fas is a cell surface receptor that induces apoptosis in sensitive cells when bound by Fas ligand (FasL). Granulosa and theca cells can express both Fas and FasL and expression varies with follicle development during the estrous cycle. The Fas pathway is highly regulated in ovarian cells and is modulated by growth factors and cytokines. Bovine granulosa cells from preovulatory follicles that are exposed to an LH surge in vivo become resistant to FasL-induced and serum withdrawal-induced apoptosis. Specific aim I is to determine whether resistance to apoptosis is mediated by: A. Withdrawal from the cell cycle induced by cell cycle regulatory proteins and/or B. Induction of the progesterone receptor and subsequent progesterone receptor-mediated effects on the cell cycle. Specific aim II is to determine the mechanism for inhibition of FasL-induced apoptosis of bovine granulosa cells by growth factors. In specific aim III the effect of modulating the cell cycle on susceptibility of granulosa cells to apoptosis will be determined. Specific aim IV is to test the hypothesis that estradiol inhibits FasL-induced apoptosis of granulosa cells by modulating the cell cycle. Relationships among aromatase expression, cyclin D2 expression, granulosa cell proliferation and escape from apoptosis during selection of the dominant follicle will be determined. An understanding of follicle atresia is essential to allow development of improved methods of fertility control, treatment of infertility and enhancement of fertility. Understanding pathways that promote or prevent susceptibility of ovarian cells to apoptosis may lead to development of novel therapies for ovarian and other cancers.